1. Field of the Invention
The present invention relates to a thin-film coating apparatus for coating a film-forming coating solution on a surface of a material to be treated such as a semiconductor wafer, a metal plate, a ceramic plate, a printed-circuit board, or a glass plate.
2. Description of the Relevant Art
Apparatus having a spinner for coating a surface of a material such as a semiconductor wafer with a photoresist or a diffusion material are known from Japanese Laid-Open Patent Publication No. 53(1978)-72464 and U.S. Pat. Nos. 3,538,883 and 4,528,934.
In the disclosed coating apparatus, the spinner is disposed in a tubular casing which is open upwardly. When a material to be processed is placed on the upper surface of the spinner, the material is attracted to the upper surface of the spinner under vacuum developed in a vacuum hole. A coating solution is dropped from an upper nozzle onto the material surface. At the same time, the spinner is rotated to rotate the material therewith to spread the dropped coating solution uniformly over the material surface under centrifugal forces.
The coating solution dropped from the nozzle is required to be of uniform nature, e.g., uniform density, for example, at all times. However, the coating solution may change its own properties or characteristics because of its chemical nature. Where the coating solution contains antimony, for example, the coating solution absorbs moisture in an atmosphere or air over the material, changing the properties of antimony.